Field of the Invention
The present invention relates to a polishing method and apparatus for polishing a surface of a substrate such as a semiconductor wafer by relative movement between the surface of the substrate and a polishing pad on a polishing table while the substrate is pressed against the polishing pad.
Description of the Related Art
In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). In the chemical mechanical polishing, while a polishing liquid (slurry) containing abrasive particles, such as silica (SiO2), ceria (CeO2) or the like, therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad and polished by using a polishing apparatus.
The polishing apparatus which performs the above-mentioned CMP process includes a polishing table having a polishing pad, and a substrate holding apparatus, which is referred to as a top ring or a polishing head, for holding a semiconductor wafer (substrate). When the semiconductor wafer (substrate) is polished with such a polishing apparatus, the semiconductor wafer is held and pressed against a surface (polishing surface) of the polishing pad under a predetermined pressure by the substrate holding apparatus while a polishing liquid (slurry) is supplied from a polishing liquid supply nozzle onto the polishing pad. At this time, the polishing table and the substrate holding apparatus are respectively rotated to bring the semiconductor wafer into sliding contact with the polishing surface, so that the surface of the semiconductor wafer is polished to a flat mirror finish, as disclosed in Japanese laid-open patent publication No. 2007-75973.
As described above, the polishing apparatus polishes the substrate by rotating the polishing table while the polishing liquid (slurry) is supplied from the polishing liquid supply nozzle onto the polishing pad. Therefore, there is a problem that mist of slurry supplied onto the polishing pad is scattered around. Further, after polishing of the substrate, water polishing of the substrate or cleaning of the substrate is performed by rotating the polishing table while pure water (deionized water) is supplied from the polishing liquid supply nozzle onto the polishing pad. Therefore, there is a problem that mist of pure water or the like supplied onto the polishing pad is scattered around. In this manner, the interior of the polishing apparatus is such an environment as to cause mist of slurry, pure water or the like, or water droplets to be scattered, and thus the scattered mist of slurry or the like is attached onto various portions in the polishing apparatus. If the attached mist is dried, the abrasive particles are agglomerated and fall onto the surface of the polishing pad during polishing, causing scratches on the surface of the substrate.
Accordingly, in the CMP process, there is a risk that the scratches due to agglomerate of the particles such as slurry are increased, thus causing a lowering of the yield. The scratches are mainly caused by falling of the agglomerated abrasive particles onto the polishing pad. As a method for preventing the fallen abrasive particles from entering between the polishing pad and the substrate, it is common practice to take measures at the time of dressing of the polishing pad. For example, a dressing speed is lowered, or cleaning for washing the abrasive particles away with a mixed fluid of a liquid and a gas, or the like by an atomizer is performed after dressing.
In order to remove the above-described agglomerated abrasive particles, existing on the polishing pad, as much as possible, the longer cleaning time of the polishing pad by the atomizer is more preferable. However, in the conventional polishing apparatus, the dressing step of the polishing pad or the cleaning step of the polishing pad by the atomizer has been set in a polishing recipe. Therefore, it is necessary to prolong the cleaning time by altering the polishing recipe so as to lengthen the cleaning time of the polishing pad by the atomizer, and thus there is a problem to lower a throughput extremely.
The inventors of the present invention have reviewed various steps which have been conducted based on the polishing recipe in the polishing apparatus for the purpose of lengthening the cleaning time of the polishing pad (polishing surface) without lowering the throughput, and obtained the following knowledge. Specifically, after one substrate such as a semiconductor wafer is polished, there is a substrate transferring process for removing the polished substrate from the top ring and loading a new substrate on the top ring.
The inventors of the present invention have focused on the fact that there is a so-called idle time, at the time of the substrate transferring process, during which no process is performed on the polishing table, and have considered the possibility to prolong the cleaning time by cleaning the polishing pad during the idle time. In this case, it is considered to add a recipe of “execute cleaning of the polishing pad during the time until the polishing recipe is re-executed”. However, when an executive instruction of the polishing recipe is made from a controller, the polishing recipe becomes in execution, and thus the completion of the polishing recipe cannot be detected by the polishing recipe itself, resulting in continuing the check whether the polishing recipe has been completed or not while the polishing recipe itself is being executed. In other words, if it is set as “during the time until the polishing recipe is re-executed”, because neither the completion of the previous polishing recipe nor the start of a subsequent polishing recipe can be detected, the state where there is no other way than continuing the cleaning of the polishing pad, is continued. Accordingly, when “cleaning of the polishing pad” is added to the polishing recipe, the cleaning time is forced to be set, thus lowering the throughput.
Further, separately from the polishing recipe, it can be considered to have such a setting as “after completion of the polishing recipe, execute cleaning of the polishing pad for a predetermined time” in advance. However, the time between the polishing recipes is not constant because various substrates are supplied into the polishing apparatus, i.e. a variety of polishing recipes are executed. Accordingly, setting the cleaning time of the polishing pad each time for each substrate is troublesome and time-consuming. Further, if the cleaning time is not set each time, the cleaning time has to be set to the minimum time between respective polishing recipes, and therefore the idle time between the polishing recipes cannot be utilized to the utmost limit.